The Bray native said that he was close to giving up and grew increasingly tired clinging to a tree stump in the middle of the crocodile-infested waters.
Dara was taking part in a charity challenge for Red Nose Day when he tumbled out of the boat, was swept down the river and managed to hold onto the tree.
The father of two and his rowing partner Olympic athlete Philips Idowu were separated from their teammates in the terrifying incident and had to wait for almost an hour on the Zambezi River to be rescued.
Spice Girl Melanie C, comedian Jack Dee, BBC Radio 1 DJ Greg James and actress Chelsee Healey are all taking part in the trial which involves paddling for up to eight hours a day during the BT Red Nose Challenge: Hell and High Water.
Dara (40) said that he was desperately trying to hold on to the tree in the face of extremely strong currents and was just beginning to tire when the guides eventually reached him.
"It became a calculation of 'I can hold myself up against this' but it is about two-and-a-half, three knots, which is like standing into a 90mph gale," he said.
"You can do it, but you will eventually get tired so you are thinking is it a good idea and also you have no idea what is underneath," he added.
During the 111km journey, the crew face rapids known as Gnashing Jaws of Death, The Washing Machine and Oblivion on their way to the world's largest waterfall, Victoria Falls.
Dara said he has tried white water rafting before but this was much more terrifying.
"Any fun and exhilaration has gone and it has been replaced with blind panic," he said.
Luckily Dara escaped with a few scrapes and bruises. But it was the second day of excitement for him.
On their first night in the Zambian jungle, he heard what he believed to be gunshots in the distance.
The challenge will see the celebs camping on cliff-tops and riverbanks as they follow the course of the challenging river.
There was trouble for Jack Dee and Melanie C yesterday, who ended up trapped beneath their canoe when it capsized and had to be rescued.
Radio 1 DJ Greg James said: "We went on some rapids with two per canoe and it all went horribly wrong," he said.